The present invention relates to a solid electrolytic capacitor comprising a conductive polymer as a solid electrolyte.
A conventional solid electrolytic capacitor comprises an electrode on the anode side composed of a film forming metal, such as aluminum or tantalum, coated with an oxide film; a solid electrolyte, such as manganese dioxide or TCNQ (7,7,8,8-tetracyanoquinodimethane) salt, deposited on the oxide film; and an electrode on the cathode side composed of a conductive metal layer or the like and provided on the reverse side of the oxide film.
However, the use of manganese dioxide as the solid electrolyte has drawbacks such as damage to the oxide film of the electrode on the anode side and poor restorability of the oxide film by manganese dioxide.
By contrast, the use of a TCNQ salt as the solid electrolyte has advantages such as high conductivity by virtue of usual powdery crystal form, freedom from the above described damage to the oxide film and superiority to manganese dioxide in the oxide film restoration.
However, since the conductivity of the TCNQ salt is fixed, it is difficult to realize a solid electrolytic capacitor complying with desired electrical characteristics.
For this reason, a conductive polymer was used as a solid eletrolyte formed on the oxide film to develop a solid electrolytic capacitor free from the damage to the oxide film and capable of providing desired electrical characteristics such as a resistance loss which can be freely set in an appropriate range.
Examples of this type of solid electrolytic capacitor known in the art include those described in Japanese Patent Laid-Open Nos. 61-10230/1986, 61-47621/1986, 60-70719/1985, 60-245111/1985, 60-245209/1985, 60-250614/1985, 60-244017/1985, 61-2315/1986, 61-47625/1986, 61-22614/1986, 61-22613/1986, 60-22311/1985, and 60-17909/1985.
In these solid electrolytic capacitors, use is made of an electrode comprising an oxide film formed on the surface of film-forming metal and, disposed thereon, a conductive polymer through electrolytic polymerization or chemical polymerization.
However, in these conventional electrolytic capacitors, since the conductive polymer layer is formed on the oxide film layer in a laminated form, it is difficult to successively adhere the oxide film layer to the conductive layer, so that a small space is formed between these layers. This unfavorably brought about a problem of a lowering in the capacity.